用Jva生成GUID

在项目里加入common-loging.jar

 /**
* @author ccadmin
*
* TODO To change the template for this generated type comment go to
*/
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;
import java.util.Random;

public class RandomGUID extends Object {
    protected final org.apache.commons.logging.Log logger = org.apache.commons.logging.LogFactory
       .getLog(getClass());

    public String valueBeforeMD5 = "";
    public String valueAfterMD5 = "";
    private static Random myRand;
    private static SecureRandom mySecureRand;

    private static String s_id;
    private static final int PAD_BELOW = 0x10;
    private static final int TWO_BYTES = 0xFF;

    /*
     * Static block to take care of one time secureRandom seed.
     * It takes a few seconds to initialize SecureRandom.   You might
     * want to consider removing this static block or replacing
     * it with a "time since first loaded" seed to reduce this time.
     * This block will run only once per JVM instance.
       */

    static {
       mySecureRand = new SecureRandom();
       long secureInitializer = mySecureRand.nextLong();
       myRand = new Random(secureInitializer);
       try {
          s_id = InetAddress.getLocalHost().toString();
       } catch (UnknownHostException e) {
          e.printStackTrace();
       }

    }


    /*
     * Default constructor.   With no specification of security option,
     * this constructor defaults to lower security, high performance.
     */
    public RandomGUID() {
       getRandomGUID(false);
    }

    /*
     * Constructor with security option.   Setting secure true
     * enables each random number generated to be cryptographically
     * strong.   Secure false defaults to the standard Random function seeded
     * with a single cryptographically strong random number.
     */
    public RandomGUID(boolean secure) {
       getRandomGUID(secure);
    }

    /*
     * Method to generate the random GUID
     */
    private void getRandomGUID(boolean secure) {
       MessageDigest md5 = null;
       StringBuffer sbValueBeforeMD5 = new StringBuffer(128);

       try {
          md5 = MessageDigest.getInstance("MD5");
       } catch (NoSuchAlgorithmException e) {
          logger.error("Error: " + e);
       }

       try {
          long time = System.currentTimeMillis();
          long rand = 0;

          if (secure) {
             rand = mySecureRand.nextLong();
          } else {
             rand = myRand.nextLong();
          }
          sbValueBeforeMD5.append(s_id);
          sbValueBeforeMD5.append(":");
          sbValueBeforeMD5.append(Long.toString(time));
          sbValueBeforeMD5.append(":");
          sbValueBeforeMD5.append(Long.toString(rand));

          valueBeforeMD5 = sbValueBeforeMD5.toString();
          md5.update(valueBeforeMD5.getBytes());

          byte[] array = md5.digest();
          StringBuffer sb = new StringBuffer(32);
          for (int j = 0; j < array.length; ++j) {
             int b = array[j] & TWO_BYTES;
             if (b < PAD_BELOW)
                sb.append('0');
             sb.append(Integer.toHexString(b));
          }

          valueAfterMD5 = sb.toString();

       } catch (Exception e) {
          logger.error("Error:" + e);
       }
    }

    /*
     * Convert to the standard format for GUID
     * (Useful for SQL Server UniqueIdentifiers, etc.)
     * Example: C2FEEEAC-CFCD-11D1-8B05-00600806D9B6
     */
    public String toString() {
       String raw = valueAfterMD5.toUpperCase();
       StringBuffer sb = new StringBuffer(64);
       sb.append(raw.substring(0, 8));
       sb.append("-");
       sb.append(raw.substring(8, 12));
       sb.append("-");
       sb.append(raw.substring(12, 16));
       sb.append("-");
       sb.append(raw.substring(16, 20));
       sb.append("-");
       sb.append(raw.substring(20));

       return sb.toString();
    }


      // Demonstraton and self test of class
      public static void main(String args[]) {
        for (int i=0; i< 100; i++) {
          RandomGUID myGUID = new RandomGUID();
          System.out.println("Seeding String=" + myGUID.valueBeforeMD5);
          System.out.println("rawGUID=" + myGUID.valueAfterMD5);
          System.out.println("RandomGUID=" + myGUID.toString());
        }
      }


}

UUID是指在一台机器上生成的数字，它保证对在同一时空中的所有机器都是唯一的。通常平台会提供生成UUID的API。UUID按照开放软件基金会(OSF)制定的标准计算，用到了以太网卡地址、纳秒级时间、芯片ID码和许多可能的数字。由以下几部分的组合：当前日期和时间(UUID的第一个部分与时间有关，如果你在生成一个UUID之后，过几秒又生成一个UUID，则第一个部分不同，其余相同)，时钟序列，全局唯一的IEEE机器识别号（如果有网卡，从网卡获得，没有网卡以其他方式获得），UUID的唯一缺陷在于生成的结果串会比较长。关于UUID这个标准使用最普遍的是微软的GUID(Globals Unique Identifiers)。